In practice, this three phase power calculator gives you the fast numbers you need before you size a breaker or pull wire. Additionally, it also works as a single phase power calculator: enter voltage, current and power factor (PF), then solve for kW, kVA, kVAR or amps. Therefore, it’s tuned for 120/240 V and 208/240/277/480 V jobs.
Single / Three-Phase Power Calculator
Convert between P (kW), Q (kvar), S (kVA), and current (A) in single- or three-phase systems.
Result
- P (kW):
- S (kVA):
- Q (kvar):
- I (A):
- Per-phase P (kW/phase):
- Per-phase I (A/phase):
* For three-phase, enter line-to-line voltage V_LL. Formulas: S = √3 · V_LL · I, P = S · PF.
For three-phase: this tool reports total 3φ power. Approx. per-phase P ≈ P/3. For 3φ 4-wire wye, line current equals phase current.
For education and pre-design checks only. Verify with applicable codes and field conditions.
Three phase power calculator — quick start
Why it matters
in real jobs, mixing up kW vs kVA or forgetting PF leads to change orders, nuisance trips, and callbacks. Therefore, doing the power-triangle math up front saves both time and money.
How to use three phase power calculator
- System — pick Single-phase or Three-phase.
- Solve for — choose what you need: kW, kVA, kVAR or Amps.
- Enter inputs — voltage (use line-to-line for three-phase), the known current or power, and PF (0–1).
- Calculate — you’ll get an answer plus the other triangle values. If something looks off, adjust PF or verify whether you used VL-L vs VL-N.
Tip: For motors, PF varies with loading. As a result, nameplate PF or measured PF gives better amp estimates than guessing 1.0.
Power-triangle refresher (kW, kVA, kVAR)
- kW (P) — real power that does the work (heat, torque, light).
- kVA (S) — apparent power seen by the source.
- kVAR (Q) — reactive power from magnetizing/charging currents.
- PF = kW / kVA. Therefore, for a given kW, a lower PF means higher amps.
Core formulas (balanced systems):
- Single-phase:
- kW = V × I × PF
- kVA = V × I
- Three-phase (use line-to-line voltage VL-L):
- kW = √3 × VL-L × I × PF
- kVA = √3 × VL-L × I
- Reactive: kVAR = √(kVA² − kW²) = kW × tan(arccos PF)
Field examples you can sanity-check
- Amps from kW (3ϕ 480 V): 10 kW at PF 0.90 → I ≈ 10,000 / (√3 × 480 × 0.90) ≈ 13.4 A.
- kW from amps (1ϕ 240 V): I = 40 A, PF 0.95 → kW = 240 × 40 × 0.95 = 9.12 kW.
- kVAR from kW & PF: 20 kW at PF 0.80 → kVAR = 20 × tan(arccos 0.80) ≈ 15 kVAR.
- Heads-up: If your three-phase voltage is 208 V (wye), remember it’s line-to-line. Otherwise, using 120 V will under-estimate amps by roughly √3.
When to use three phase power calculator vs other tools
- Sizing feeders and services — start here to get kW/kVA and Amps, then jump to your Wire Size or Voltage Drop tool.
- Motor / EVSE planning — use actual PF if you have it; in addition, consider inrush and duty cycle when selecting OCPD and conductors.
- Generator / UPS estimates — convert kW ↔ kVA quickly and pick a sensible PF; meanwhile, leave margin for starting loads.
- Panel balancing — calculate each large load; consequently, you’ll keep phases even and the neutral cool.
Common mistakes (and how to avoid them)
- Using VL-N on three-phase — the math expects VL-L. Double-check your meter readout.
- Assuming PF = 1 — lighting with modern drivers may be close, but motors and welders rarely are.
- Confusing hp with kW — don’t forget motor efficiency and PF; hp × 0.746 gives shaft kW only.
- Unbalanced loads — this calculator assumes balanced three-phase; if not, solve phase by phase.
Practical workflow (fast and repeatable)
- Estimate PF from nameplate or past jobs.
- Solve for amps, then check breaker and conductor against ampacity and temperature corrections.
- Therefore, if voltage drop is near your target, upsize the conductor now rather than fixing callbacks later.
- Finally, document assumptions (PF, efficiency, duty) in your notes or quote.
Extended reading & internal resources about three phase power calculator
- Voltage Drop Calculator
- Wire Size & Ampacity →
/wire-size-ampacity - Panel upgrades & breaker selection →
/panel-upgrade - AFCI/GFCI protection basics →
/afci-gfci-guide
References (open in a new tab)
- Power triangle and PF basics
- Engineering Toolbox — common line voltages and relationships (VL-L vs VL-N)
Disclaimer: This power calculator is for education and pre-design checks. Final selections must follow the NEC and local amendments, equipment listings, and your AHJ or project engineer.
FAQ
Use line-to-line (VL-L) for these formulas. Otherwise, your amps will be under-estimated by about √3.
Lighting with modern drivers may be ~0.95–0.99; small motors might be 0.75–0.90; welders and VFDs vary. Therefore, confirm whenever possible.
No—efficiency is separate from PF. For motors, convert horsepower to shaft kW (hp × 0.746), then divide by efficiency to get input kW before applying PF.
Yes. Meanwhile, use 120/240 V for residential and 208/240/277/480 V for commercial; the math updates instantly.
Quick fundamentals check before you rely on this calculator
I’m Engineer Tsai. One more question, since it trips people up on three-phase math specifically: for a balanced three-phase load, why do you multiply by √3 instead of just 3? (Short answer: because the three line-to-line voltages aren’t in phase with each other, so you can’t just add them directly — √3 is what that phase relationship actually works out to. If that made sense immediately, you’re in good shape.)
If it didn’t, or you’d rather find out exactly which fundamentals are solid before you trust a calculator with real wiring, I put together a free Electricity Fundamentals Mock Exam. It’s a self-practice quiz for reviewing basics like this — not an official certification or licensing exam, and it doesn’t replace your local code or a qualified electrician’s judgment.
